The NIDDK has identified the genetics of type 2 diabetes mellitus (T2D) as one of five high priority areas for research. Specifically Studies using quantitative statistical methods to identify diabetes genes in human populations. and Development of genetic resources, patient samples and methods for studying genetic linkage for diabetes. We propose here a novel two pronged strategy to identify genes for diabetes susceptibility (prediabetes). This powerful multilayered approach combines genome-wide gene expression with genetic linkage and association screening. In brief, the two Aims of this study are as follows. Aim 1: A high resolution association study of gene expression in vivo in three key tissues, adipose tissue, skeletal muscle and mononuclear cells (MNCs) in 40 matched pairs of unrelated subjects who differ by fasting specific insulin (FSI) a surrogate marker of insulin resistance (IR). Gene expression will be measured under fasted conditions in the three tissues, and in response to insulin stimulation during an insulin clamp for skeletal muscle and MNCs. Aim 2: A family-based linkage study of gene expression in MNCs from 1,000 subjects, who have previously been genotyped, from two large ongoing genetic studies, the Veterans Administration Genetic Epidemiology Study (VAGES) and the San Antonio Family Diabetes/Gallbladder Disease Study (SAFDGS). We will perform preliminary functional evaluation of the strongest candidate genes identified in the study. We previously reported strong evidence in those studies of linkage of IR traits with chromosome 6q23. We hypothesize that there is differential expression of genes involved in inflammation and insulin action in adipose tissue, skeletal muscle and leukocytes from subjects with differential risk for prediabetes, as manifested by IR, and that this pattern of differential gene expression contributes to T2D susceptibility. RELEVANCE TO PUBLIC HEALTH: Type 2 diabetes mellitus (T2D) is the leading cause of blindness, end stage renal disease, non-traumatic amputations, and it increases the risk for other serious medical disorders such as hypertension, dyslipidemia, and atherosclerotic cardiovascular disease, and is the fifth leading cause of disease-related death in the US. Thus, T2D represents a huge public health problem that is projected to worsen in the coming decades, particularly as the mean age of the population increases. Insulin resistance (IR), usually associated with obesity, is a major risk factor for the development of T2D, however, the genes which predispose some individuals to these diseases are unknown. Identification of IR genes will greatly improve our understanding of how these diseases occur and provide new biomarkers of disease and treatment targets for future drug therapy and hope for alleviation of the accelerating diabetes/obesity epidemic.